MEXICO CITY — Mexican authorities are investigating a battle between two suspected gangs that left at least 20 bodies, 17 of them burned, in a border town near where US President Donald Trump will visit on Thursday to win support for his plan to build a wall.

Mexican President Andres Manuel Lopez Obrador said at his daily morning news conference that initial information pointed to a “battle between two groups,” and that security officials would later provide further information.

He has justified that demand by saying that undocumented migrants, criminals and illegal drugs have been pouring across the border, although statistics show illegal immigration has fallen to a 20-year low, while many drugs are believed to enter through legal ports of entry.

A Mexican security official said that authorities discovered 20 bodies on Wednesday, 17 of them burned, outside Ciudad Miguel Aleman, which is about 56 miles from McAllen, across the Rio Grande river. Five burned vehicles were also found near the bodies, the security official said.

A separate state security official said on Thursday that 21 bodies had been found at the site.

Tamaulipas has become one of the most violent states in Mexico, convulsed by gangs fighting to control drug trafficking, extortion rackets and the exploitation of migrants.

Tens of thousands of people have been killed in Mexico during years of fighting between security forces and warring drug cartels.